The metabolism of sucrose, galactose and lactose by lactic acid bacteria were studied. Sucrose-PTS, sucrose 6-phosphate hydrolase and mannofractokinase activities were characterized in streptococcus lactis. Sucrose induced expression of the PTS and hydrolase activities but mannofructokinase was expressed after growth in the presence of sucrose or any growth carbohydrate not transported by a PTS mechanism. A system for conjugal transfer of lactose plasmids among Lactobacillus casei strains was developed. From the results of this, and other studies, it appeared that the plasmids encoded the lactose-PTS and phospho-Beta-galactosidase. These results have been confirmed by the molecular cloning of lactose plasmid DNA into Escherichia coli. Recombinant clones containing a 7.9 kBp insert of actobacillus plasmid DNA in the PTS I site of pBR322 expressed cloned phospho-Beta-galactosidase activity. Lactobacillus lactose plasmids were found to have considerable DNA-DNA homology even though the restriction endonuclease digestion fragment patterns varied greatly. A unique galactose-specific PTS has been isolated from L. case.